Peptides or peptide analogues are useful, for example as medicaments. One example of such peptide is Cetrorelix which can be used for the treatment of endometriosis and uterine fibroids in women, and benign prostatic hypertrophy in men. Cetrorelix is a gonadotrophin releasing hormone antagonist (GnRH antagonist) which has the following sequence.
(SEQ ID NO: 1)Ac-D-Nal-D-Cl-Phe-D-Pal-Ser-Tyr-D-Cit-Leu-Arg-Pro- D-AlaNH2
Persilylation techniques are discussed in EP-A-184243, in Callens, IBC's 2nd International Conference on Peptide Technologies, Rogozhin et al. Isvestija Akademia Nauk SSSR, Seriya Khimecheskaya, No. 3, p. 657-660 (1978) and Kricheldorf, Liebigs Ann. Chem. 763, p. 17-38 (1972).